Heating device and method for operating the same

ABSTRACT

A heating device includes: a fluid reservoir; a heat exchanger whose feed line is hydraulically connected to the fluid reservoir geodetically deeper than its return line; a pump situated in the feed line or the return line; a bypass hydraulically connected to the feed line and to the return line, the bypass bypassing the heat exchanger and the pump; and a three-way valve situated in the connection of the bypass to the feed line or in the connection of the bypass to the return line. Based on a comparison of a setpoint temperature with a first fluid temperature determined in the return line between the heat exchanger and the bypass, the three-way valve is switched into a first switch position in which the bypass is at least partially open, or the three-way valve is switched into a second switch position in which the bypass is closed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a heating device for heating a fluid in a fluid reservoir.

2. Description of the Related Art

Different heating devices for heating a fluid in a fluid reservoir are known from the related art, thus, for example, for providing a supply of hot water.

One variant hereby provides heating of the fluid within the reservoir using a heat exchanger. In another variant, cooler fluid is initially removed from a lower area of the fluid reservoir, then heated outside of the reservoir, and finally returned into an upper area of the fluid reservoir. Based on a temperature-dependent density of the fluid, the fluid stratifies in the fluid reservoir from warm above to cold below. A pump is necessary in the feed line or the return line of the heat exchanger in order to convey the fluid through the heat exchanger.

The problem here is that the fluid in the upper area of the fluid reservoir should have a certain setpoint temperature for the removal of fluid by a consumer. If the fluid flowing in the feed line of the heat exchanger is very cold, then the temperature in the return line is always still below the setpoint temperature. It consequently takes a relatively long time until fluid with the setpoint temperature is available in the draw-off zone of the fluid reservoir. This is inconvenient for the consumer. In addition, the fluid temperature in the draw-off zone may increase above the setpoint temperature if the fluid in the feed line to the heat exchanger is already relatively hot. This may result in scalding and other damages. These problems may indeed by avoided by adjusting the heat output at the heat exchanger; however, heating devices, for example heat pumps, have a maximum efficiency at a defined heat output. Operation outside of the optimum results in increased costs and is not ecologically worthwhile.

It is therefore the object of the present invention to eliminate the disadvantages of the related art and to develop a heating device as well as a method for operating the same, using which a high degree of efficiency of the heating device is respectively achieved and at the same time fluid with a setpoint temperature may always be removed from a fluid reservoir. Simplicity, low production costs, and reliability in operation should be kept in mind.

In a heating device including a fluid reservoir, a heat exchanger, whose feed line is hydraulically connected to the fluid reservoir geodetically deeper than its return line, and a pump which is situated in the feed line or the return line, the present invention provides that a bypass is hydraulically connected to the feed line and to the return line, the bypass bypassing the heat exchanger and the pump, and a three-way valve is situated in the connection of the bypass to the feed line or in the connection of the bypass to the return line.

The design according to the present invention with the three-way valve and the bypass is now suitable for heating fluid circulating via the bypass up to a setpoint temperature. Only when the temperature of the fluid reaches the setpoint temperature is the fluid fed back into the fluid reservoir. Having arrived here, the fluid with the setpoint temperature stratifies in the draw-off zone at the top of the fluid reservoir. Thus, a heating unit corresponding with the heat exchanger may always be operated in its optimum operating range, so that the operating costs are low, and a high degree of efficiency and eco friendliness is achieved. Furthermore, the necessary components, like the three-way valve and the bypass, are relatively inexpensive in relation to the total costs of the heating device and the operating costs of the same. The heat exchanger is preferably situated outside of the fluid reservoir. As a result, different heating units, such as, for example, heating units fired with fossil fuels, heat pumps, and solar thermal systems, may be straightforwardly coupled to the heat exchanger. The bypass should also be situated outside of the fluid reservoir, since it is easily accessible here. For the same reasons, the pump and/or the three-way valve should be situated outside of the fluid reservoir.

One refinement of the present invention provides that the heat exchanger is a condenser of a heat pump. Heat pumps in particular have a very narrow optimum operating range. However, by using the three-way valve and the bypass according to the present invention, the heat pump may always be operated in this optimum operating range without the occurrence of deviations from the setpoint temperature.

In order to achieve an automated application of the heating device, the three-way valve is activatable according to one variant of the present invention. It may thus be automated and thereby conveniently changed to different switch positions.

In one refinement of the heating device, a first temperature sensor is situated in the return line between the heat exchanger and the bypass for detecting a first fluid temperature in the return line. Based on the ascertained first fluid temperature, the three-way valve may be switched in real time. The setpoint temperature may thus be continuously maintained.

Furthermore, one refinement of the heating device provides that the return line empties into a draw-off zone situated geodetically at the top in the fluid reservoir. In addition, a second temperature sensor may be provided here for detecting a second fluid temperature in the draw-off zone. The emptying into the upper area prevents convection flows within the fluid reservoir, so that the temperature stratifications of the fluid are clearly separated from each other. As a result, the efficiency of the heating device is high, since the fluid in the feed line is preferably cool. Thus, a maximum temperature difference is present in the heat exchanger. It is particularly favorable here if the feed line is connected to the fluid reservoir geodetically at the bottom.

In order to prevent a backflow of fluid out of the fluid reservoir into the return line, regardless of the installation position or operating situation, it is advisable to situate a check valve in the return line between the fluid reservoir and the bypass. This is recommended in particular if switch positions of the three-way valve are provided, in which the bypass is only partially opened.

Furthermore, one variant of the present invention provides that the three-way valve is activated by a control unit, in which a setpoint temperature is stored, and which is connected to the first temperature sensor in a data communicating way. A control unit of this type is particularly suited for automated operation of the heating device, since it may adjust the three-way valve as a function of the setpoint temperature.

The present invention additionally relates to a method for operating a previously described heating device, in which the pump is activated and fluid flows through the heat exchanger. Heat is thereby transferred to the fluid in the heat exchanger. In the return line between the heat exchanger and the bypass, a determination of a first fluid temperature takes place, which is subsequently compared with a setpoint temperature. If the first fluid temperature is lower than the setpoint temperature, the three-way valve is switched into a first switch position, in which the bypass is at least partially open. If, in contrast, the first fluid temperature is higher than the setpoint temperature, the three-way valve is switched into a second switch position, in which the bypass is closed.

Using this method, it is now possible, regardless of the heat output and the associated amount of heat transferred to the fluid in the heat exchanger, to constantly heat the fluid to the setpoint temperature. A heater, and thus the entire heating device, may therefore always be operated in an ecological and cost-efficient optimum operating conditions.

Due to a partial opening of the bypass, the fluid in the feed line may be continually pre-heated and, at the same time, fluid at the setpoint temperature is fed into the fluid reservoir. This means that the three-way valve distributes the fluid heated to the setpoint temperature quantitatively to the bypass and to the return line to the fluid reservoir.

One refinement of the method is characterized in that the pump is deactivated if a third fluid temperature in the feed line upstream from the bypass is higher than the setpoint temperature. In particular, if this is the case, then the fluid reservoir is already heated to the setpoint temperature up to the draw-off zone of the feed line and a continuation of the heating is not possible. The deactivation results in an efficient operation of the heating device.

If a heater is coupled exclusively to the heat exchanger, then the heater should also be deactivated. Conversely, the activation of the pump may be made a function of the temperature of the fluid in the fluid reservoir at the draw-off level of the feed line. If the temperature falls below the setpoint temperature by a certain amount, then an activation is appropriate. To keep the number of temperature sensors low, it is therefore advisable to situate the third temperature sensor at the draw-off level of the feed line.

From the control technological standpoint, the bypass is completely opened in the first switch position of the three-way valve in a simple variant of the present invention. The fluid thereby circulates completely via the bypass until it reaches the setpoint temperature. It is subsequently conveyed via the return line into the fluid reservoir, and cooler fluid flows in afterward, which is subsequently again circulated completely via the bypass until it reaches the setpoint temperature.

To prevent a fast toggling back and forth of the three-way valve, one refinement of the method provides that a hysteresis is taken into account during a change between the switch positions of the three-way valve. In this case, the setpoint temperature must always be exceeded by a certain amount before the switch position is changed.

It is not always necessary to provide fluid at the setpoint temperature in the fluid reservoir. Therefore, the method may be supplemented to the effect that an override switching of the three-way valve into the second switch position occurs if maintaining the setpoint temperature in a draw-off zone situated geodetically on top in the fluid reservoir is not necessary. For this purpose, the consumer may determine the times of day at which an increased convenience requires that the fluid has the exact setpoint temperature. At other times of day, a circulation via the bypass is dispensed with, whereby fluid is then conveyed through the heat exchanger at a preferably low temperature. Consequently, a high temperature difference is present in the heat exchanger. The efficiency of the heating device is thus particularly high.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a heating device, in which a three-way valve in a first switch position is situated between the bypass and the return line.

FIG. 2 shows an image section of the heating device shown in FIG. 1, however with the three-way valve being in the second switch position.

FIG. 3 shows a heating device, in which a three-way valve in a first switch position is situated between the bypass and the feed line.

FIG. 4 shows an image section of the heating device shown in FIG. 3, however with the three-way valve being in the second switch position.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a heating device 1. This includes a fluid reservoir 2 filled with fluid F. Fluid F may be removed from a draw-off zone 9, which is situated geodetically on top in fluid reservoir 2, via an extraction line 30. A second temperature sensor 12 for detecting a second fluid temperature T2 in the draw-off zone 9 is provided here. A feed line 31 empties into the geodetically lower end of fluid reservoir 2. Fluid F flows in through this feed line when fluid F is extracted via extraction line 30.

Furthermore, heating device 1 includes a heat exchanger 3, whose feed line 4 is hydraulically connected to fluid reservoir 2 geodetically deeper than its return line 5. In particular, return line 5 empties into fluid reservoir 2 in the area of its geodetic top side. In contrast, feed line 4 empties into fluid reservoir 2 in the area of its geodetic bottom side.

A pump 6 for transporting fluid F is situated in feed line 4. Furthermore, a bypass 7, which is hydraulically connected to feed line 4 and return line 5, thereby bypasses heat exchanger 3 and pump 6. A three-way valve 8, which is controllable, is situated in the connection of bypass 7 to return line 5.

Heat exchanger 3, three-way valve 8, and bypass 7 are situated outside of fluid reservoir 2. A first temperature sensor 11 for detecting a first fluid temperature T1 in return line 5 is situated between heat exchanger 3 and bypass 7 in the area of return line 5.

It further shows that heat exchanger 3 is a condenser 21 of a heat pump 20. Heat pump 20 thereby includes a heat pump circuit for a coolant K, into which condenser 21 is integrated. In addition, an evaporator 22 is integrated into the heat pump circuit. Moreover, a compressor 23 is situated in the flow direction of coolant K upstream from condenser 21, and an expansion valve 24 is situated in the flow direction downstream from condenser 21. Coolant K and fluid F thus flow in a counterflow through condenser 21, whereby coolant K transfers heat to fluid F.

Three-way valve 8 is activated by a control unit 10, in which a setpoint temperature TS is stored. Control unit 10 is connected in a data-communicating way to first temperature sensor 11 for determining switch positions S1, (S2, cf. FIG. 2) of three-way valve 8. Furthermore, connections exist of control unit 10 to compressor 23 of heat pump 20, to pump 6, and also to second and a third temperature sensors 12, 14. Third temperature sensor 14 is used to detect third fluid temperature T3 in feed line 4 upstream from bypass 7. Alternatively to the position shown outside of fluid reservoir 2, third temperature sensor 14 may also be positioned in the area of the extraction opening of feed line 4.

Control unit 10 is therefore suited to carry out a method for operating heating device 1, in which initially pump 6 is activated and fluid F flows through heat exchanger 3. Additionally, control unit 10 activates compressor 23 of heat pump 20. Pressurized by compressor 23, coolant K, thereby elevated to a high temperature level, transfers heat to fluid F in heat exchanger 3. With the aid of first temperature sensor 11, control unit 10 determines first fluid temperature T1 in return line 5 between heat exchanger 3 and bypass 7. First fluid temperature T1 is compared with the stored setpoint temperature TS.

Based on the result of the comparison, control unit 10 switches three-way valve 8 into a first switch position S1 if first fluid temperature T1 is lower than setpoint temperature TS. In first switch position S1, shown in FIG. 1, bypass 7 is completely open. The section of return line 5 emptying into fluid reservoir 2 is, in contrast, closed by three-way valve 8. Correspondingly, fluid F circulates via bypass 7 and heat exchanger 3.

If, in contrast, first fluid temperature T1 is higher than setpoint temperature TS, control unit 10 switches three-way valve 8 into a second switch position S2, as is apparent in FIG. 2. FIG. 2 hereby shows a section A from FIG. 1, whereby, departing from first switch position S1 shown in FIG. 1, second switch position S2 is represented. In second switch position S2, bypass 7 is closed. Fluid F, heated to setpoint temperature TS, is then conveyed into draw-off zone 9 of fluid reservoir 2, and cooler fluid F from fluid reservoir 2 flows in via feed line 4.

The control unit advantageously takes a hysteresis into account during a switch between switch positions S1, S2 of three-way valve 8 in order to prevent fast toggling back and forth when first fluid temperature T1 fluctuates around setpoint temperature TS.

With the aid of control unit 10, pump 6 may be additionally deactivated if third fluid temperature T3 in feed line 4 is higher upstream from bypass 7 than setpoint temperature TS.

Furthermore, an override switching of three-way valve 8 into second switch position S2 may be provided by control unit 10 if maintaining setpoint temperature TS in draw-off zone 9 is not necessary. Time periods may be stored by a consumer in control unit 10 for this purpose.

FIG. 4 shows a section B from heating device 1 shown in FIG. 3, which corresponds in large part to that of FIG. 1. In the specific embodiment of FIG. 3, deviating from FIG. 1, three-way valve 8 is situated in the connection between bypass 7 and feed line 4. Moreover, an additional check valve 13 is situated in return line 5 between fluid reservoir 2 and bypass 7.

FIG. 4, like FIG. 2, shows a second switch position S2 of three-way valve 8. In FIG. 2, as also in FIG. 4, bypass 7 is completely closed by three-way valve 8.

Deviating from FIG. 1, bypass 7 is only partially open according to the first switch position S1 of three-way valve 8 as shown in FIG. 3. At the same time, the section of feed line 4 leading from fluid reservoir 2 to three-way valve 8 is at least partially open. Therefore, a mixing of heated fluid F from bypass 7 with cool fluid F from feed line 4 takes place in three-way valve 8. Control unit 10 thereby controls three-way valve 8 in such a way in first switch position S1 that fluid F in return line 5 constantly has setpoint temperature TS. 

1-10. (canceled)
 11. A heating device, comprising: a fluid reservoir; a heat exchanger, wherein a feed line of the heat exchanger is hydraulically connected to the fluid reservoir geodetically deeper than a return line of the heat exchanger; a pump situated in one of the feed line or the return line; a bypass hydraulically connected to the feed line and to the return line, wherein the bypass bypasses the heat exchanger and the pump; and a three-way valve situated one of (i) in the connection of the bypass to the feed line, or (ii) in the connection of the bypass to the return line.
 12. The heating device as recited in claim 11, wherein the heat exchanger is a condenser of a heat pump.
 13. The heating device as recited in claim 12, wherein the three-way valve is a controllable valve.
 14. The heating device as recited in claim 11, wherein a first temperature sensor is situated in the return line between the heat exchanger and the bypass for detecting a first fluid temperature in the return line.
 15. The heating device as recited in claim 14, wherein the three-way valve is activated by a control unit storing a setpoint temperature, wherein the control unit is connected in a data-communicating way to the first temperature sensor.
 16. A method for operating a heating device having: a fluid reservoir; a heat exchanger, wherein a feed line of the heat exchanger is hydraulically connected to the fluid reservoir geodetically deeper than a return line of the heat exchanger; a pump situated in one of the feed line or the return line; a bypass hydraulically connected to the feed line and to the return line, wherein the bypass bypasses the heat exchanger and the pump; and a three-way valve situated one of (i) in the connection of the bypass to the feed line, or (ii) in the connection of the bypass to the return line, wherein the method comprises: a) activating the pump and flow of fluid through the heat exchanger, b) transferring heat to the fluid in the heat exchanger, c) determining a first fluid temperature in the return line between the heat exchanger and the bypass, d) comparing the first fluid temperature with a setpoint temperature, e1) if the first fluid temperature is lower than the setpoint temperature, switching the three-way valve into a first switch position in which the bypass is at least partially open, and e2) if the first fluid temperature is higher than the setpoint temperature, switching the three-way valve into a second switch position in which the bypass is closed.
 17. The method as recited in claim 16, further comprising: f) deactivating the pump if a third fluid temperature in the feed line upstream from the bypass is higher than the setpoint temperature.
 18. The method as recited in claim 16, wherein the bypass is completely open in the first switch position of the three-way valve.
 19. The method as recited in claim 16, wherein a hysteresis is taken into account during a change between the switch positions of the three-way valve.
 20. The method as recited in claim 17, further comprising: g) override switching of the three-way valve into the second switch position if it is not necessary to maintain the setpoint temperature in a draw-off zone situated geodetically on top in the fluid reservoir. 